1. Field of the Invention
The present invention relates to a control device of an internal combustion engine.
2. Description of the Related Art
To optimize the air-fuel ratio of an air-fuel mixture burned in a combustion chamber of an internal combustion engine, it is necessary to accurately estimate the amount of air charged in the combustion chamber when the intake valve closes (hereinafter referred to as the “cylinder air charge amount”). Normally, the cylinder air charge amount is estimated from a large number of sensors such as a flow rate sensor (air flow meter) and a large number of maps using as arguments the outputs from these sensors. Here, if using maps to estimate the cylinder air charge amount, the necessary number of maps and the number of the arguments become great. Along with this, the steps for compliance at the time of preparing the maps end up becoming extremely great. Therefore, in recent years, the use of numerical calculation models expressed by equations based on fluid dynamics etc. has been studied so as to reduce the number of maps and the number of arguments to calculate the cylinder air charge amount.
Japanese Unexamined Patent Publication (Kokai) No. 2002-70633 describes a device for calculating the cylinder air charge amount using such numerical calculation models. The device of Japanese Unexamined Patent Publication (Kokai) No. 2002-70633 utilizes the fact that, from the law of the conservation of mass, the value of the amount of air flowing into an intake pipe minus the amount of air accumulated in the intake pipe is equal to the amount of air charged in the cylinder, in order to calculate the cylinder air charge amount. Specifically, it subtracts from the amount of throttle valve air passage detected by an air flow meter etc. the amount of change of the intake pipe air calculated based on the air pressure in intake pipe detected by a pressure sensor etc. and uses the result as the cylinder air charge amount.
By the way, since the intake valves corresponding to the cylinders successively open, pulsation occurs in the air pressure in intake pipe (intake pulsation). However, if the device of Japanese Unexamined Patent Publication (Kokai) No. 2002-70633 were to take into consideration the pulsation of the air pressure in intake pipe in calculating the cylinder air charge amount, the calculation would end up becoming complicated, so the actually occurring pulsation of the air pressure in intake pipe is ignored in calculating the cylinder air charge amount. That is, despite the fact that the air pressure in intake pipe actually changes greatly due to intake pulsation, the amount of change in the intake pipe air is calculated excluding the change in the air pressure in intake pipe due to pulsation by calculation.
However, in actuality, the pulsation of air pressure in intake pipe is closely related to the cylinder air charge amount for each cylinder. If it were possible to calculate the cylinder air charge amount utilizing this pulsation, it would be possible to calculate the cylinder air charge amount more accurately.